#include<iostream>
#include<vector>
using namespace std;

class Solution
{
public:
    int climbStairs(int n)
    {
        if(n == 0)
            return n;
        vector<int> dp(n+1);
        dp[1] = 1;
        dp[2] = 2;
        for(int i = 3; i <= n; i++)
        {
            dp[i] = dp[i-1] + dp[i-2];
        }
        return dp[n];
    }
};


int main()
{
    Solution s;
    cout << s.climbStairs(5) << endl;
    return 0;
}